1. Field of the Invention
The present invention relates to a gas component detector which may suitably be used in exhaust gas purifying systems employing a three-way catalyst of, for example, automobiles.
2. Description of the Prior Art
Gas component detectors known in the art include the one as disclosed in U.S. Pat. No. 3,959,765. In this case, a detector is constituted by a detector element having a sintered body of a transition metal oxide, a pair of electrodes buried in the detector element, and a ceramic body having a pair of narrow holes to accomodate therein the pair of electrodes and a pair of large penetrating holes to accomodate therein a pair of lead pins for picking up a change in electrical resistance value of the detector element to outside. An electrically conducting glass is used between the electrodes and the lead pins to obtain the electrical conduction therebetween. Further, the detector has a housing with threads to enable it to be mounted on an exhaust pipe or the like.
By further study of the gas component detectors having the construction conventionally known as mentioned above, it has been found that some problems still exist. For example, conductive glass is used to electrically connect the lead pins and the electrodes. However, since it is necessary to push in the lead pins and to apply pressure on the conductive glass when it is in a melted state for the purpose of filling the conductive glass uniformly in the connecting portion, lead pins having a large diameter must be used in order to widen an area of the lead pins to be applied with pressure. Thus, a large ceramic body is needed, and consequently, the construction of the detector itself becomes large.
Further, there are problems as mentioned below, in the gas component detector which is known from U.S. Pat. No. 4,001,758.
(1) The ceramic body and the housing are fixed by caulking using a washer and a ring. Therefore, the caulking force is apt to be insufficient, becomes loose and thus insufficiently airtight, and also sometimes the ceramic body or the detector element is broken at the time of caulking.
(2) The electrodes are not fixed in the trough holes. Therefore, the electrodes start vibrating when vibrations are transmitted to the electrode from outside. Consequently, the electrodes can be cut or broken. Also, in case the electrodes are made with a large diameter, the thickness of the detector element connected with the electrodes becomes larger and the response deteriorates.